渗透胁迫等因素对春小麦幼苗硝酸还原酶活性的影响

本文研究了渗透胁迫、热胁迫、外源脯氨酸和脱落酸对春小麦幼苗 NR 活性的影响.结果表明,NR 对水分胁迫极为敏感,随胁强增加,活性持续下降;解除胁迫后,一般24h 内活性即能恢复.NR 对热胁迫也很敏感,当温度高于正常生长温度10℃时,活性即迅速下降。外源脯氨酸能够减缓胁迫条件下 NR 活性的下降。外源脱落酸在胁迫条件下加剧 NR 活性的下降。     

黄米醇溶蛋白对小鼠胆固醇代谢的调节作用

比较了分别饲喂酪蛋白、大豆分离蛋白、黄米醇溶蛋白小鼠的血清总胆固醇、高密度脂蛋白胆固醇、低密度脂蛋白胆固醇,甘油三酯浓度和动脉硬化指数,旨在评价黄米醇溶蛋白对小鼠胆固醇代谢的特定作用。结果显示:黄米醇溶蛋白(添加1.82%Lys和0.23%Trp)能显著提高小鼠血清高密度脂蛋白胆固醇浓度(P<0.05),降低动脉硬化指数;但体外实验表明:黄米醇溶蛋白不能抑制羟甲基戊二酸单酰辅酶A(HMG-CoA)还原酶的活性,即不能抑制胆固醇的合成。线性回归分析得出黄米醇溶蛋白对小鼠血清胆固醇代谢的调节作用与其蛋氧酸与甘氨酸含量之比、疏水性氨基酸、含硫氨基酸含量密切相关。     

大肠杆菌guaC基因的克隆及高效表达

以E.coli MC4100染色体DNA为模板使用PCR扩增技术克隆了鸟苷酸还原酶基因guaC，该基因全长1044bp，编码相对分子质量为37ku的蛋白质。将该基因直接克隆于PET—16b质粒的T7启动于下游，得到质粒pEXP1。转化E．coli BL21(DE3)，经异丙基硫代半乳糖苷(IPTG)诱导，获得了高效的表达。含表达质粒的菌体胞内粗提液经酶活分析表明，鸟苷酸还原酶的活性为不含质粒的宿主菌的80-85倍。     

人细胞色素P450氧化还原酶的克隆表达和抗体的制备

细胞色素P450还原酶(CPR)是人细胞色素P450酶系的电子供给者,对后者活性的发挥起到重要作用.本研究将从人胚胎cDNA文库中得到的人CPR的编码基因,连接入pT7450表达载体中,在大肠杆菌BL21(DE3)中高效表达并纯化.每升发酵液可得到纯化蛋白49 mg,占总蛋白含量的10%,以细胞色素C为底物检测酶活性,比活为65 u/mg.利用纯化的CPR作为抗原,常规免疫纯系大耳家兔,获得高效价、高特异性的抗血清,抗体滴度为1∶200 000(ELISA法),纯化后抗体应用于不同组织中CPR含量的评价,证明重组CPR及其抗体可用于细胞色素P450的体外药物代谢及细胞色素P450与CPR作用机理的研究.     

Nitric oxide synthase reduces nitrite to NO under anoxia

Cultured bEND.3 endothelial cells show a marked increase in NO production when subjected to anoxia, even though the normal arginine pathway of NO formation is blocked due to absence of oxygen. The rate of anoxic NO production exceeds basal unstimulated NO synthesis in normoxic cells. The anoxic release of NO is mediated by endothelial nitric oxide synthase (eNOS), can be abolished by inhibitors of NOS and is accompanied by consumption of intracellular nitrite. The anoxic NO release is unaffected by the xanthine oxidase inhibitor oxypurinol. The phenomenon is attributed to anoxic reduction of intracellular nitrite by eNOS, and its magnitude and duration suggests that the nitrite reductase activity of eNOS is relevant for fast NO delivery in hypoxic vascular tissues. Received 20 August 2006; received after revision 21 September 2006; accepted 8 November 2006     

香根草对重金属镉的积累及耐性研究

通过香根草的水溶液培养,研究了不同浓度的镉(Cd)对香根草的生理和生态的影响.结果表明:香根草富集的Cd主要被累积在根内,最高富集系数达到24.06%.溶液Cd浓度与香根草根内Cd的累积量显著正相关(r=0.987 4),与根的耐性指数呈显著负相关(r=-0.943 6).低浓度Cd(≤1 mmol.L-1)处理使根系活力和硝酸还原酶(NR)活力随时间呈现先升后降的趋势,中、高浓度Cd(≥1.5 mmol.L-1)处理使根系活力呈显著下降的趋势,且浓度越高,下降幅度越大.化学形态分析表明,在香根草体内Cd的NaCl提取态占绝对优势,在根和茎叶内的平均占52.06%和64.03%.可以认为香根草在Cd胁迫下其氮代谢、呼吸作用,植物的生长发育受到一定程度抑制,但其对Cd仍具有较强的耐性和富集能力.     

All in the family: aldose reductase and closely related aldo-keto reductases

Aldose reductase catalyzes the first step in the polyol pathway and is thought to be involved in the pathogenesis of diabetic complications. In addition to polyol synthesis, aldose reductase may have multiple other activities that intersect with signal processing and oxidative defense mechanisms. Multiple aldose reductase-like proteins have been discovered to have structures and catalytic properties that broadly overlap those of aldose reductase. This chapter will summarize new insights into properties and functions of aldose reductase and closely related members of the aldo-keto reductase enzyme superfamily.     

Functional, biochemical and genetic diversity of prokaryotic nitrate reductases

Prokaryotic nitrate reduction can serve a number of physiological roles and can be catalysed by a number of biochemically distinct nitrate reductases. Three distinct nitrate reductase classes can be indentified in prokaryotes, NAS, NAR and NAP. NAS is located in the cytoplasmic compartment and participates in nitrogen assimilation. NAR is usually a three-subunit complex anchored to the cytoplasmic face of the membrane with its active site located in the cytoplasmic compartment and is involved in anaerobic nitrate respiration. NAP is a two-subunit complex, located in the periplasmic compartment, that is coupled to quinol oxidation via a membrane anchored tetraheme cytochrome. It shows considerable functional flexibility by participating in anaerobic respiration or redox energy dissipation depending on the organism in which it is found. The members of all three classes of enzymes bind the bis-molybdopterin guanine dinucleotide cofactor at the active site, but they differ markedly in the number and nature of cofactors used to transfer electrons to this site. Analysis of prokaryotic genome sequences available at the time of writing reveals that the different nitrate reductases are phylogenetically widespread.     

硝酸还原酶和可溶性蛋白对东北三省蒙古栎种源生长性状的影响

本文研究了东北三省25个蒙古栎种源的硝酸还原酶和可溶性蛋白与生长性状的关系．不同生长性状的蒙古栎种源,硝酸还原酶活性和可溶性蛋白含量上都存在着显著的差异,并且同一种源呈现明显的季节变化．试验结果表明生长性状与所研究的两个理化指标之问存在显著的正相关,即高、径生长好的种源,硝酸还原酶活性和可溶性蛋白含量高;硝酸还原酶活性大的种源,可溶性蛋白含量也高,可以为林木育种提供参考．本试验中,集安种源在两项生理指标中含量均最高,可作为优质种源进行推广．     

Structure/function analysis of a critical disulfide bond in the active site of l-xylulose reductase

l-Xylulose reductase (XR) is involved in water re-absorption and cellular osmoregulation. The crystal structure of human XR complemented with site-directed mutagenesis (Cys138Ala) indicated that the disulfide bond in the active site between Cys138 and Cys150 is unstable and may affect the reactivity of the enzyme. The effects of reducing agents on the activities of the wild-type and mutant enzymes indicated the reversibility of disulfide-bond formation, which resulted in three-fold decrease in catalytic efficiency. Furthermore, the addition of cysteine (>2 mM) inactivated human XR and was accompanied by a 10-fold decrease in catalytic efficiency. TOF-MS analysis of the inactivated enzyme showed the S-cysteinylation of Cys138 in the wild-type and Cys150 in the mutant enzymes. Thus, the action of human XR may be regulated by cellular redox conditions through reversible disulfide-bond formation and by S-cysteinylation. Received 25 January 2009; received after revision 12 February 2009; accepted 16 February 2009 H.-T. Zhao, S. Endo: These two authors contribute equally to this work.